The present invention relates generally to electric switches and, more particularly, to rotary electric switches.
Rotary electric switches are well-known in the art and are widely used to control alternating current circuits for a variety of applications. For example, rotary electric switches are particularly useful in connection with multispeed electric motors for household appliances, such as food processors, blenders, fans and the like.
Rotary electric switches usually include a hollow housing. The housing is usually made of plastic and includes a recessed base and a cover member. A rotatable contactor is centered in the base and is controlled by a switch handle or shaft. A plurality of resilient stationary contacts are positioned edgewise in the base around the rotatable contactor for making and breaking the several circuits through the switch.
The rotatable, or movable, contactor is constructed of a conductive material, such as brass. The rotatable contactor is typically annular shaped and has a thickness in the range of approximately 0.040 inches to approximately 0.062 inches. The rotatable contactor is shaped to include a central opening which is sized to fit over an annular boss formed on the recessed base. The rotatable contactor is also shaped to include an outer periphery which includes a plurality of integrally formed contact projections which serve the purpose of making or breaking a connection with the stationary contacts to form a closed or open circuit, respectively.
Each stationary contact is generally in the shape of a Z, where the ends of the Z represent a locking tongue and a spring contact finger which are joined together by an intermediate arm. The two bends in the Z shaped stationary contact, one where the locking tongue engages the intermediate arm and the other where the intermediate arm engages the contact finger, are supported in opposite pockets in the base so that the intermediate arm will flex slightly to distribute the bending stresses exerted on both the locking tongue and the spring finger.
The locking tongue on each stationary contact provides the switch with the capability of implementing push-in wire terminals. In particular, a wire to be connected is pushed through a wire receiving opening formed in the base, the wire receiving opening being partially covered by the free end of the locking tongue of the stationary contact. Once forced through the wire receiving opening, the wire will displace the locking tongue away from the opening which enables the wire to be fed into the base. Once the wire is sufficiently pushed through the opening, the locking tongue engages the side of the wire and effectively locks the wire within the switch between the stationary contact and a sidewall of the housing. When a pulling force is exerted to remove the wire from the switch, the wire tends to carry the tongue with it so that the locking tongue is pushed harder against the wire wedging it against the side wall of the plastic housing, the force of the wedging pressure increasing in proportion to the pulling force exerted on the wire.
In U.S. Pat. No. 5,750,947 to C. P. Rao et al, there is disclosed a rotary electric switch with conductive plates. The rotary electric switch has push-in wire terminals and includes a hollow plastic housing having a recessed base and a cover, the base having a plurality of wire receiving openings. A plurality of resilient stationary contacts are positioned in the base, each resilient stationary contact being generally Z-shaped and having a locking tongue at one end, an intermediate arm, and a spring finger at the opposite end from the locking tongue. Each resilient stationary contact is positioned in the base with its locking tongue overlying a wire receiving opening in a side wall in the housing. A rotatable contactor is mounted in the base between the spring fingers of the resilient stationary contacts. A plurality of conductive plates are disposed in the base, one conductive plate associated with each resilient stationary contact, each conductive plate contacting the resilient stationary contact at a location on its intermediate arm and in addition preventing a wire inserted into the opening from touching the sidewall of the housing. The housing includes a number of projections and standoffs to provide adequate spacing between current carrying components on the switch.
Rotary electric switches of the type described above are frequently used in commerce and have a maximum rating of approximately 13 amps. However, rotary electric switches of the type described above often experience a notable drawback. Specifically, due to the relatively narrow thickness of the rotatable contact, the contact surface area of the contact projections is limited. As a consequence, it has been found that running electricity through the relatively small contact surface area of the contact projections can result in a significant mechanical wear in the stationary contact. Significant mechanical wear in the stationary contact can cause the spring finger, and in particular the contact surface area of the spring finger, to wear away.
Wearing away of the spring finger of the stationary contact can create a significant air gap, or separation, between the rotatable contact and the plurality of stationary contacts. The creation of an air gap between the rotatable contact and the plurality of stationary contacts can result in a lost electrical connection between the rotatable contact and the stationary contacts, thereby rendering the switch nonfunctional. The creation of an air gap between the rotatable contact and the plurality of stationary contacts can also result in the flow of electricity through the air gap, or arcing, which is undesirable and destructive.